Heel (3)
'heel' is the definition.
(both can mean a dishonourable person)
This is all the clue.
(Other definitions for cad that I've seen before include "Dishonourable man of decadent sort" , "Rogue" , "he's no gent" , "One behaves dishonourably" , "An Englishman who behaves dishonourably, a rotter" .)
(Other definitions for kitten that I've seen before include "Beatrix Potter's Tom, say" , "Young Tom perhaps" , "Little Tom, perhaps" , "Baby rabbit" , "Immature cat" .)